Disk drive suspension interconnects for hard disk drives typically have three layers, namely, a stainless steel foil (a spring metal layer) which provides mechanical properties for the suspension, two or more conductive signal traces which provide electrical connection between the read/write head slider and the termination pads of the suspension, and a dielectric layer which provides electrical insulation between the stainless steel foil and the conductive traces. The stainless steel foil acts as a support layer for the dielectric layer and the conductive traces. The suspension interconnect defines a flexible electrical circuit.
Suspension circuits commonly have termination pads at the ends of the circuits located on flying or unsupported metallic conductors. Such unsupported metallic conductors are typically referred to as “flying leads.” Examples thereof are disclosed in U.S. Pat. No. 7,468,866 issued to Yang, et al.; in U.S. Patent Publication No. U.S. Patent Application Publication No. 2006/0163078 by Peter; and in copending application Ser. No. 12/540,870, filed Aug. 13, 2009 and entitled “Resilient Flying Lead and Terminus for Disk Drive Suspension.”
One purpose of the flying lead region is to provide access to both surfaces of the conductive lead. The flying leads typically terminate at three locations. Electrical contacts to the flying leads are made using various methods common to microelectronics packaging. The most prevalent termination practices relative to location are: solder ball bonding when terminating to the read-write head; conductive epoxy when terminating to a PZT in a dual stage actuated suspension; and thermosonic bonding at the input/output terminations near the primary actuator. The flying leads have metallic conductors that are unsupported by the dielectric layer that normally separates the conductive signal traces from the other conductive layers and the substrate or support layer, such as the stainless steel foil. The flying leads therefore typically lack the stiffness provided by the underlying dielectric layer and stainless steel layer. The flying leads may be supported by dielectric or other materials on opposing sides of the span, or in the case of read-write terminations may be of a cantilevered configuration and be supported from a single side.
FIG. 2 in U.S. Pat. No. 7,142,395 (Swanson) shows a flying lead region 50. The flying leads are over portions of the tail that are free of the spring metal base. In particular, Swanson shows a test pad portion 46, for example, on the side of the flying leads away from the suspension. Such a test pad portion is typically used to test the completed suspension assembly. If it is found that a read-write head (also referred to as a slider) on a suspension assembly is defective, the head is replaced by parting the flexure tail bond and replacing the head. On the other hand, if the read/write head passes the tests, the test pad portion is cut off and the suspension is integrated into a completed disk drive unit. Swanson discloses methods of manufacturing integrated lead head suspension flexures of the type having conductors on a spring metal layer and having a flying lead region.
FIGS. 6, 8, and 12, for example, of Swanson show a multi-layered flying lead region. Swanson at col. 5, lines 25-27 discloses that the flying lead region of the conductive lead may be wider than other portions of the conductive lead. Additionally, FIGS. 15, 16, 17, 18 and 19, for example, show flying lead regions with alternative reinforcement members.
During the disk drive manufacturing process, the flying leads can be used for test purposes, as mentioned above and as is also discussed in U.S. Pat. No. 7,110,222 (Erpelding). In particular, Erpelding describes integrated lead suspensions and tail pad terminations of those suspensions. The tail pads can be electrically connected via soldering or thermosonic bonding.
U.S. Pat. No. 5,666,717 (Matsumoto) discloses a number of processes, such as cladding, sputtering, vacuum deposition and ion plating, which can be used to manufacture flexures.
U.S. Pat. No. 7,518,830 (Panchal et al.) discloses a flying lead 53 in FIG. 3. The flexure of Panchal has traces on both sides of the spring metal layer. The trace can be electrically connected together by a via that extends through the spring metal layer and the dielectric material. Panchal discusses multi-circuit flexure designs that purportedly reduce flexure width, minimize temperature and humidity effects on mechanical performance, and achieve higher electrical performance.
U.S. Pat. No. 5,883,759 (Schulz) discloses flying leads at reference numeral 54. The flying leads electrically connect the conductive traces to the contact pads of the magnetic head.
Fragile unsupported leads, and particularly flying leads, are prone to damage during assembly or testing or when separating the ultrasonic bonding terminal or solder bonding terminal for rework. In recent years, as the thickness of the copper conductor layer has decreased from about 12 μm to about 7 μm, the leads have become even more fragile, making rework even more difficult.
Stacked conductor configurations are also known, and an example thereof is disclosed in U.S. Pat. No. 5,883,759 (Schulz). Referring to the Abstract of Schulz, first and second conductive trace layers at least partially overlap one another and are sufficiently proximate to one another to reduce inductance of an electrical interconnect. The interconnect electrically connects a magnetic head and read/write circuitry in a disk drive.
Stacked sets of conductors are also disclosed in U.S. Pat. No. 5,587,479 (Bennin et al.) in the paragraph bridging columns 12 and 13 and in FIG. 14 thereof.
Stacked trace constructions, where two copper traces are separated by a thin polyimide layer, can exhibit improved electrical performance over non-stacked trace constructions. In a stacked trace configuration, the trace pairs are separate and not electrically connected. One trace carries a positive half of the signal (+) and the other trace carries a negative half of the signal (−). Stacking the two halves of a differential pair in this manner can reduce the transmission line impedance as compared to side-by-side conductors.